Cosmarium connatum
Brébisson ex Ralfs, 1848
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Simmelried
Phylogenetic tree: Cosmarium connatum
Diagnosis:
- semi-cells sub-circular with slightly narrowed base
- apical view circular
- length 50–90 µm, width 42–74 µm
- very broad isthmus
- sinus widely open
- cell wall covered with fine pores
- a ring of larger pores near isthmus
- 2 pyrenoids per semi-cell
I frequently find Cosmarium connatum in the Simmelried between floating aquatic plants and in the uppermost mud layer. The cells are very easy to identify due to their very wide isthmus. The semi-cells are broad elliptical. The cell wall is finely punctured, and the semi-cells have a ring of larger pores only at their base, near the isthmus (s. fig. 1 b).
Cosmarium connatum can only be confused with Cosmarium pseudoconnatum. However, this species is somewhat smaller (30–75 µm) and contains four pyrenoids in each semi-cell.
Fig. 1 a-b: Cosmarium connatum. L = 68 µm. Two focal planes of a specimen in DIC. Near the isthmus each semi-cell has a ring of larger pores (RP). PY = pyrenoids. Obj. 100 X.
Fig. 2 a-b: Cosmarium connatum. L = 68 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 100 X.